MTI (Moving Target Indication) radar systems have been built for many years, based on . The simple MTI delay-line canceller shown in Fig.4 is an example of a. Download scientific diagram | Block Diagram for Double Delay Line Canceller from publication: Implementation of MTI based Pulse compression Radar system . The MTI radar uses Low Pulse Repetition Frequency (PRF) to avoid range ambiguities. . Y. &. D. E. S. I. G. N. I. I. S. T. Effect of delay line canceller on the signal.
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USA – Delay line canceller for radar system – Google Patents
An example embodiment of the invention will now be described with dadar to the accompanying drawings in which: We know that a single delay line canceller consists of a delay line and a subtractor. Similarly, a difference in gain between the two channels 35 and 36 results in an output signal from the subtractor network 45 which is coupled through the AND gate 5 to the amplitude cancelle 51 where it is referenced against a signal from the voltage controlled crystal oscillator FIGURE 1 is a block schematic diagram of part of a radar system utilizing a delay line canceller of the present invention; and.
Homodyne FMCW radar range resolution effects with sinusoidal nonlinearities in the frequency sweep.
The block diagram of Double delay line canceller is shown in the following figure. Velay the stalo 19 is common to both the upconverter mixer 1S and the downconvertcr mixer 31, IF signals reflected from stationary objects which do not undergo any Doppler shift will be identical in frequency to those at the output of the carrier gate 15 as shown in FIGURE 2D.
If the time delay in the delayed channel 36 relative to that in the undelayed channel 3S is not equal to the period of the alternating current pulse signal from the generating means 11, successive signals will not completely cancel im the output of the subtractor network We will get the following mathematical relation from the second delay line canceller. However, when very short pulse intervals are transmitted having only a few cycles of alternating current componenta difference in deoay between the alternating current components of the two signals would result in substantial residual signals which appear as moving targets on the 4radar display.
We will get the following mathematical relation from first delay line canceller. An example embodiment of the invention will now be described with reference to the accompanying drawings in which:.
When a Doppler phase shift is encountered due to refiection from a moving object, the time delay between the reception of successive pulse signals will not equal that of the delay line 41, and the IF signals reflected from the moving object will not be identical in frequency to those at the output of the carrier gate The outputs 43 and 44 are connected to the input of a subtractor network 45 which is connected at its output to the IF output To insure this, the present invention provides that during the transmission interval, alternating current pulse signals from the carrier gate 15 are coupled to the input 34 of the delay line canceller 13 through the OR gate Complete cancellaion will only occur when the period of the signal from the carrier gate 15 is equal to the time delay of the delay line 41, the initial phase of the alternating current component of each pulse signal at D is a constant, the received IF signals reflected from targets are identical in frequency to those at the output of the carrier gate 15, and the gains of the two channels 35 and 36 are equal.
A phase error signal will then be coupled from the phase demodulator 53 and after passing through the integrating amplifier 55 will be used to control the frequency of the voltage controlled crystal oscillator The output of the carrier gate 15 is connected to an input of an upconverter mixer 1’8 which is driven by a stable local oscillator or stalo The amplifier 30 is connected to an input of a down-converter mixer 31 which is also driven by the stalo Delay line cancellers can be classified into the following two types based on the number of delay lines that are present in it.
Radar Systems Delay Line Cancellers
Also, the gain of the two channels 35 and 36 is monitored and maintained equal on a pulse signal frequency basis. In addition, since the carrier gate 15 is triggered by the output of a frequency divider 17 which in turn is controlled by the voltage controlled crystal oscillator 14, the phase of the alternating current component of each pulse signal, illustrated in FIGURE 2D, will be constant.
In a typical embodiment, this oscillator 14 produces a signal dleay a frequency of If two such delay line cancellers are cascaded together, then that combination is called Double delay line canceller. It the additional channels are adequately matched in performance to those of the delay line canceller 13, the single amplitude error signal derived from the amplifier 52 can be used to control the gains of all the channels in the chain.
It is nothing but the frequency response of the single delay line canceller. This produces a control signal at the cancellers output which is used to control the periodI of the transmitted pulse signals so that the period is fully synchronized with the time delay encountered in the canceller.
The pulse generator 16 is, in turn, connected to a frequency divider 17, the output of which is connected to the other input of the carrier gate The signals from the channel outputs 32 and 33 are then subtracted by the substractor network Still another problem is that if the period of the cancellerr pulse signals does not equal the time delay in the delay line canceller, the delayed and undelayed signals reflected from stationary objects will not arrive in time coincidence at the output of the canceller, and a residual signal will result.
The output of the amplitude demodulator 51 is coupled through an integrating amplifier 52, the output of which is used to control the variable gain network The frequency response characteristics of both double delay line canceller and the cascaded combination of two delay line cancellers are the same. One way of accomplishing this is to delay the reflected signal due to one transmitter pulse by rwdar time interval equal to canxeller period of the pulses and then lime it from the cancwller signal due to the succeeding pulse.
The output of subtractor is applied as input to Full Wave Rectifier. What is claimed is: The advantage of lune domain delay line canceller is that it can be operated for all frequency ranges.
Kennedy and Edgar J.
Radar Systems – Delay Line Cancellers
The input 34 of the delay line canceller 13 is connected to two channels; an undelayed channel 35 which includes a phase equalizer 40, and a delayed channel 36 which includes a delay line 41 and a variable gain network Thus, reilected signals from stationary objects will be cancelled out and only those from moving objects will appear on the radar display.
When the signals are reflected from stationary objects, the time delay in the channel 36 which includes the delay line 41 is equal to the period between successive transmitted pulses.
In one embodiment of such a system, the invention includes means for controlling the frequency of the alternating current component of the alternating current pulse signals so that it is an integral multiple of the reciprocal of the delay line period.